In high voltage power systems such as those handling 100 kV and above, proper insulation of equipment such as inductive devices is necessary so as to ensure the safe operation thereof. Moreover, due to the high powers involved, energy losses generate such quantities of heat in for instance inductive elements that cooling may be necessary.
Windings in high voltage inductive devices such as reactors and transformers are typically cooled by means of a dielectric fluid such as transformer oil, which can absorb the heat generated in the winding. When oil is absorbing heat in the winding, it has to escape from the winding and be replaced by cool oil which can absorb additional heat. Therefore, an oil channel can be provided in an insulation system which insulates the winding. Insulation systems may for instance be provided with an oil channel of horizontal oil ducts which are arranged in a horizontal zig-zag pattern at the upper end and at the lower end of the winding.
JP61150309 discloses an oil-circulating transformer winding for obtaining high cooling efficiency. The oil enters the cooling structure at one end of the winding and exits the cooling structure at the opposite end of the winding via vertical oil passages which are formed by insulating tubes for vertical oil flow so as to allow oil to cool the transformer winding.
CH232439 discloses an insulation system for a transformer winding. The insulation system has barriers which allows for flow of oil in opposite directions at one end of the winding.
DE873721 also discloses an insulation system for a transformer winding. The system has barriers arranged with openings for allowing oil to flow in a zig-zag pattern in the axial direction.
A drawback with the prior art is that they do not provide sufficient dielectric properties on both ends of the winding in some cases, for example in some high voltage direct current applications (HVDC).